Integrative Approach to Elucidate the Stratigraphy and Structure of the Roberts Mountains Allochthon and the Gold Deposits That It Conceals in the Independence Range of North Central Nevada, USA

The Roberts Mountains allochthon (RMA) extends from central Idaho, through central Nevada, to southern California. It is an Early Mississippian fold-thrust belt comprised of eugeoclinal Cambrian through Devonian slope-rise siliclastics thrust eastward over age-equivalent miogeoclinal carbonate slope-shelf assemblage.

Within the Independence Range in northern Nevada, Eocene Carlin-type (disseminated auriferous pyrite) gold deposits are largely hosted in altered calcareous miogeoclinal rocks, and exposed along regional trends and in erosional windows through antiforms in the RMA. The trends and antiforms that localize the deposits are transverse to the continental margin and RMA and are thought to be underlain by fault zones inherited from Neoproterozoic rifting and subsequently inverted during Antler and/or later contraction. The gold deposits formed during pulses of Eocene extension that channeled ore fluids upward into culminations. The RMA acted as an impermeable cap rock that caused ascending ore fluids to move laterally away and into permeable reactive carbonates.

Most of the Carlin-type deposits in the windows have been located. Hence, current exploration involves drilling through the RMA and understanding of the structure and thickness of the allochthon is critical in identifying exploration targets.

We have employed a multi-disciplinary approach to help unravel stratigraphic and structural complexities within the RMA. Together with governmental, industrial and academic collaborations we have compiled field, geophysical, geochemical, geochronologic, and core/drilling data to develop a 3-D model of part of the RMA. For example, industry provided down-hole descriptions and geochemistry used for exploration targets that are an invaluable resource in identifying stratigraphic and chemo-stratigraphic relationships.

The results of this study will help guide our efforts in other parts of the RMA and in understanding how inherited basement structures impart transverse modification and along-strike discontinuities in fold-thrust belts, how Carlin-type gold deposits are localized, and how exploration-specific data can be utilized in basic geologic research.